Wobble press

ABSTRACT

In a wobble press with a first wobbling die-half (1) and an axially parallel moving second half-die (2), the wobbling motion is generated by a plurality of hydraulically actuated working pistons (5) cyclically engaging with the wobbling half-die (1). By means of the elimination of centrifugal forces by a counterweight (G) connected to the wobbling half-die (1), the precise guiding of the die-halves (1,2) by a centering disk (17) and the avoidance of a mechanical drive by using a multiple-pistons pump (20) and a hydraulic control system for the working pistons (5), it is possible to reduce undesirable rotary forces, vibration, friction and heat generation in such a way that substantially higher wobble frequencies and shorter processing times are attained at lower cost while maintaining the geometrical wobble effect owing to the higher wobble frequency, with a simple and rapidly acting control of the extent and form of higher wobble frequency, with a simple and rapidly acting control of the extent and form of the wobbling movement even during operation, thus making it possible to preselect the most suitable pressing program.

TECHNICAL FIELD

This invention pertains to a wobble press having a first die half whichis driven by a drive relative to a space axis, wobbly around a fulcrumpoint, and which includes a movable second half die axially parallelrelative to the first die half wherein the wobble drive includeshydraulic working pistons which are provided with a regular, defined,pulsating flow of a hydraulic medium and which on their part areconnected with the first die half for the generation of a wobblemovement.

STATE OF THE ART

Such a wobble press is, for example, known in CH 662983, CH 666857 or DE1652653 and serves for the production of massive parts of metal or otherrigid materials, wherein the part or the workpiece is formed between twoenveloping tools or die parts wherein, in opposition to the parallelaxial press methods the one die half carries out a rolling type ofwobbly movement. Due to the partial contact of the upper die with theworkpiece material the workpiece material can, via the wobble movement,be brought to movement with substantially less press force so that inone step substantially greater degrees of deformation and a moreexacting forming of the matrix contours may be achieved. The possiblefeed advance during contact is determined by the angle of inclination ofthe wobbling tool and is thus correspondingly limited. The magnitude ofthis advance determines the total working stroke, i.e., for the desireddegree of forming the required number of wobble passes and thecorresponding wobble frequence determines the time of forming.

In known wobble presses, using mechanical drives for the wobble movementlimits the rotational frequency or wobble frequency through a number offactors:

In the transverse setting of the wobbling tool, disturbing centrifugalforces originate which particularly emanate also from the large mass ofthe eccentric shaft and the eccentric drive components. These freeforces produce prohibitive vibrations, at higher wobble frequencies,between the tool parts, thus restricting the wobble frequency in knownwobble presses to low values.

The cup shaped bearing of the wobbling tool must in addition theretoabsorb the entire press thrust. Due to the cup shaped formation of theupper pressure bearing, the bearing pressure increases per unit area andthus considerably increases the work produced due to friction. The thusproduced frictional heat must be removed through a thin oil film fromthe bearing clearance. With increasing wobble frequency the frictionheating increases in an analog manner, which heat must be removedthrough the lubricating means. On the other hand, the narrow bearingclearance limits the through-put flow of the lubrication and coolingmeans.

The insufficient heat removal and the centrifugal forces of the offcenter mass prohibit, in known constructions, the utilization of wobblefrequencies more than approximately 600 revolutions per minute. If thepermitted advance per wobble cycle is not exceeded, workpieces of mediumdimension are turned out in forming times of approximately 4 to 5seconds with a corresponding production capacity of only 10-12 parts perminute. During the trial at this limited wobble frequency to reducedeformation time via the increase in the closing speed of the press, didhowever lead to an increase in the contact area between the workpieceand the wobble tool. In this instance, a total press force would berequired which is the same magnitude as in axially parallel presses sothat the wobble press can in this instance not provide an essentialadvantage.

DESCRIPTION OF THE INVENTION

The task of the invention is to eliminate the noted deficiencies of theprior art and to provide a wobble press which permits a continuousoperation with increased wobble frequency and a reduction of the shapingtime of a workpiece specifically also in the mid range and the warmrange.

According to the invention, this task is solved in that a first wobbledriven die half which is connected with a counterweight and is thuslyshaped and arranged that its center of gravity is moved 180° to theopposite side of the fulcrum point as the center of gravity of the firstdie half and that the product of its mass and distance to the center ofgravity from the fulcrum point corresponds approximately to the productof the mass of the first die half and the distance to the center ofgravity from its fulcrum point.

Since the center of gravity of the counterweight is moved 180° oppositeto the center of gravity of the wobbling tool and since the products ofthe mass and the distance from the center of gravity cancel each other,no centrifugal forces can occur in the light of the off center locationof the wobbling tool and the centrifugal forces are automaticallyeliminated during all wobble frequencies, wobble amplitudes and anglesof inclination.

With another variation, the compensation of the forces due to inertia ofthe wobbling tools can be achieved in that a movable mass is proposed onthe same side as fulcrum point tool. Through the movement of thecounterweight to the extent of the eccentric movement of the tool to theopposing side of the center axis the necessary counter force can beproduced whereby the movement of the counter mass can be achieved via alever structure as a function of the eccentric movement.

The invention rests upon the manifestly not considered knowledge thatthe disadvantages of the prior art can be to a large degree obviated viathe compensation of the centrifugal forces of the wobbling so that thewobble press can be operated at an increased frequency.

In a practical embodiment of the inventive wobble press, in continuousproduction, frequencies of about 2400 revolutions per minute and with areduction in the deformation time to approximately 1-1.5 seconds wereachieved without interfering vibrations. This short shaping time permitsthe expansion of wobble presses into the area of hot forming withoutapprehension that the tools, due to a long exposure time with the heatedmaterial wear uneconomically and at the same time that the material issubject to premature cooling during the shaping operation.

It is particularly advantageous to have exact guidance of the two diehalves even with off center material distribution which can be assuredin that the first die half is operatively coupled with a centering platethus producing a practically clearance free centralization with theother die half.

In a particularly advantageous further development of the presentinvention the wobble drive of the first die half has at least threewobble pistons surrounding a wobble axis which are supplied via amultiple pump periodically with a cyclically varying pressure medium.Advantageously, this cyclical variation is produced via two coactingaxial piston pumps with rotating angled wobble plates which affect anumber of pump pistons which in turn are connected via hydraulicconduits with one each of the associated wobble pistons.

BRIEF DESCRIPTION OF THE FIGURES

The invention as well as further embodiments thereof will be furtherexplained via the working examples depicted in the Figures. They show:

FIG. 1 is a wobble press in a longitudinal section taken along thewobble axis;

FIG. 2 is a cross-section of a wobble press of FIG. 1 along plane II;

FIG. 3 is a segment of the longitudinal section of the press;

FIG. 4 is a detailed representation of the elimination of centrifugalforces;

FIG. 5 is a detailed representation of the die guidance; and

FIGS. 6a-d show different possible wobble movements.

WAYS FOR THE EXECUTION OF THE INVENTION

The wobble press shown in FIG. 1, having a wobble-driven upper die half1 and an axially parallel moving lower die half 2 and a workpiece,located between both dies 1, 2 which is to be shaped, has a press frame12, with built-in support rods 15, a press slide 8 as well as ahydraulic sliding drive movable via piston 9. The press frame absorbsthe opposing force of the pressing force developed by the press slide 8or rather hydraulic piston 9. Press frame 12 or rather support rods 15is formed by an upper transom 7, a lower transom 14 and a number ofrotationally symmetrical columns 13 placed around press axis A. As isshown in FIG. 2, for example, four such columns 13 can be provided. Inplace of a column frame a box frame can also find use whereby aprismatic bed section is advantageous. The press slide 8 carries thefixed lower tool or die half and is hydraulically pressed, via piston 9against the wobbling upper die half 1 retained in a workpiece holder.

The wobble movement of the upper die half is produced through several,at least three touching working pistons 5, 6, working through thediameter of the movable tool holder in cup 3 which pistons are impactedwith a periodically sine shaped pulsating oil mass which is produced viahydraulic multiple pump with a plurality of pump piston 25, 26. Thelatter is comprised of two axial piston pumps 21 residing in the sameaxial location perpendicular to the wobble axis, each driven viaelectric motor 31, 32 with controllable revolutions. Both of these pumps21, 22 work each with a surrounding dynamically balanced wobble plate toavoid centrifugal forces with wobble plates 23, 24 having a fixedinclination relative to drive axis B, respectively C in oppositelyadjustable angle positions. Wobble plate 23, 24 cyclically move pumppistons 25, respectively 26 whose number corresponds to the number ofworking pistons 5, 6. Each pump piston 25 of one pump 21 is connectedwith the pump piston 26 of the other pump 22, in the same order, viahydraulic lines 27, 28 respectively connected and the hydraulic conduits27, respectively 28 in turn are rigidly connected with pressure conduits29, respectively, 30 of the associated work piston 5, respectively 6.

With each revolution of the pump drive shaft, respectively of wobbledisks 23, 24, respectively the flow of a pump piston pair 25, 26increases from zero at an angle of 0° to a maximum at an angle of 180°and from thereon the fluid volume is reduced until it achieves an angleof 360°. The working piston 5 which is directly connected with pumppiston 25, 26 via conduit 27, 28, 29, 30 imitates this sine-shapedmovement and transmits it to the wobbling tool wherein the stroke sizedepends upon the ratio of cross section of the pump piston to the crosssection of the wobble piston. If through corresponding control of thepump motors the phase location of the wobble plates is oppositely moved,a stepless regulation of the wobble stroke of the upper workpiece can beregulated from maximum at 0° difference of the phase locations of bothpumps through zero at a difference of the opposing phase locations of180°. The drive shafts 31, 32 of the wobble plates are driven viaseparate motors so that in view of opposing variations of theirrevolutions different forms of the wobble performance of the upperworkpiece can be achieved.

Through variation of the numbers of revolutions and the direction ofrotation of pump drive motors 31, 32 all desired forms of a wobbledevelopment can be produced. FIG. 6a shows as example a star shaped,FIG. 6b a spiral shaped, FIG. 6c a nearly linear movement in a directionof choice, and FIGS. 6d a circular wobble movement T relative to wobbleaxis A. Due to the benefit of the minimal rotating masses and theelectronic control of pump drive members 31, 32 different variations canbe programmed and can be utilized within one and the same shapingoperation under load.

With axial piston pumps of the described type high axial forces areencountered which are normally received via axial anti-frictionsbearings. With revolutions over 2,000 rpm, the life span of suchbearings is limited. With the inventive arrangement this axial load, atthe ends of the pump shaft is reciprocally supported wherein due topossible difference in the number of revolutions, a pressure bearing 33takes over the support.

The workpiece holder 4 is particularly shown in the enlarged recitationin FIG. 3, formed in a cup shape so that the wobbling die half 1 iscentered relative to fixed die half 2. Thus, the opposing pressure ofthe lower die half 1 is not absorbed in the cup shaped workpiece holder4 or its guidance 3 but rather by the hydraulic medium in workingpistons 5, 6.

Lower die half 2 is retained in press slide 8 which is movable viapiston 9. Piston 9 includes, in addition, a hydraulically actuatedejection piston 11 for workpiece 10.

FIG. 4 and 5 portray in detail the construction of the upper wobblingdie half 1 in which all centrifugal forces, produced in operation arecompensated for. The magnitude of these centrifugal forces Z_(o), on theupper die half 1, is determined through the eccentricity E_(o) of thecenter of gravity S_(o) relative to axis A. For compensation of thecentrifugal force, a counterweight G is attached below the upperwobbling die half 1 having a center of gravity displaced 180°. Theeccentricy E_(u) and the center of gravity S_(u) of counterweight G areso chosen so that a centrifugal force Z_(u) is achieved in the samemagnitude as the centrifugal force Z_(o) of die half 1. For that purposethe product of the distance E_(u) of the center of gravity S_(u) ofcounterweight G from fulcrum M is chosen preferably the same as thecorresponding product of the wobbly driven upper die half 1. Theresultant of both centrifugal forces Z_(o) and Z_(u), is perpendicularto axis A then approaches zero and is indeed independent of the angle ofinclination of the upper tool and of the wobble frequency. The momentproduced via the axial pistons of both centrifugal forces can then betaken up without difficulty via the drive of the wobble movement.

In another variation the compensation of the natural forces of thewobbling tools can be achieved in that a movable mass is provided on thesame side of the center of gravity of the tool. Through a movement ofthe counterweight to the extent of the eccentric deflection of theworkpiece to the opposing side of the central axis the required opposingforce can be achieved whereby the movement of the countermass isachieved via a lever structure as a function of the eccentricdeflection.

The described compensation of the centrifugal forces permits, togetherwith the other described requirements a striking increase in the wobblefrequence of values up to approximately 2400 revolutions per minute andpermits the reduction of the shaping time of the workpiece to a normalvalue used in drop-forging in mechanical presses, that is a noticeableincrease in manufacturing output as well as the use of increasedtemperature of about 800° to about 1100° without excessive heating ofthe tools and without premature cooling of the workpiece.

In order that counterweight G takes the least possible room and is easyto store it is advantageously made of a material of a high specificweight for example from lead or other heavy metals or tungsten carbide.

For the maintenance of the centered position of both die halves and forworkpieces with considerable unsymmetrical material distribution therigidity of the opposing guidance is of considerable importance. Inorder to reduce the clearance in the guidance of press slide 8 and topossibly eliminate the same, a direct centering is provided. For that acentering disk 17 is directly connected with the tool holder of theupper die half which practically fits without clearance on the outerdiameter of lower die half 2 and which makes a rigid connection duringthe deformation process. During the last portion of the deformationcycle lower die half 2 enters into centering disk 17 and assures evenwith noncentered workpiece material distribution the adherence of veryclose tolerances with reference to the axial displacement, that is evennonrotational-symmetrical distribution of the workpiece cross sectionassures direct tool guidance, the exact adherence of the coincidence ofthe axes of the two die halves.

Counterweight G which serves for the balancing of the centrifugal forceis in this instance shaped as a ring and connected with wobbling upperdie 1 with a plurality of spacer bolts 16. Openings or slits 16 ofdesired form, in centering disk 17 permit the swinging movement ofspacer bolts 16.

The described embodiment is particularly advantageous with hydraulicdrive since a highly stressed axial bearing is not required which athigh rotational speeds would only have a short life span. The smoothrunning is distinctly increased and higher revolutions can be achievedin continuing operation. Through changes in the speed and the directionof rotation or movement of the phases of the two pumps, the opposingmovements of both tools can readily be accommodated to technologicalrequirements and one can depending on requirement realize, withoutdifficulty, circular movements, spiral movements, vibratory movements orrotational movements wherein the extent of the wobble inclination andalso the input of the differring movement programs can be preprogrammedand controlled without the loss of time. The upsetting process can, forexample, be started with the upper tool at rest and can without delay bebrought up to the desired wobble stroke.

At the end of each testing process the warm hydraulic medium circulatingbetween the pump and the working pistons can be flushed out and possibleleakages at the end of the press piston hub can be compensated for via afilling suction valve. The pressure oil heated in the process of a presscycle can at the end of the cycle be cooled with a suitable oil cooler.

What is claimed:
 1. A wobble press comprising in combination: a firstdie half; a movable second die half axially parallel relative to thefirst die half; means for wobbly driving said first die half, having amass and a center of gravity S_(o), with regard to a longitudinalcentral axis (A) of said press, wobbly around a fulcrum point (M), saidwobble drive means including hydraulic working pistons which areprovided with a regular, defined, pulsating flow of a hydraulic medium,said hydraulic working pistons being connected with said first die halffor the generation of a wobble movement; a counterweight (G), having amass and a center of gravity (S_(u)), connected to said first wobblydriven die half, said counterweight (G) being so structured and arrangedthat the product of the mass of said counterweight (G) and theeccentricity spacing (E_(u)), of the spacing of the center of gravity.(S_(u)) of said counterweight (G), relative to longitudinal axis (A), atleast approximately corresponds to the product of the mass of said firstdie half and the eccentricity spacing (E_(o)), of the spacing of thecenter of gravity (S_(o) ) of said first die half, relative tolongitudinal axis (A), so that the centrifugal forces of both saidcounterweight (G) and said first die half at least approximatelycompensate each other.
 2. The wobble press of claim 1, wherein saidcounterweight (G) is thusly arranged that its center of gravity (S_(u))lies on the opposed side of the fulcrum (M) of the wobble movement asthe center of gravity (S_(o)) of said first die half, and that theproduct of said counterweight mass and its eccentricity spacing (E_(u))relative to the fulcrum point (M) of the wobble movement at leastapproximately corresponds to the product of the mass of said first diehalf and its eccentricity (E_(o)) relative to fulcrum point (M).
 3. Thewobble press of claim 1 wherein said counterweight (G) consists of amaterial with a high specific weight, specifically over 10 g/cm².
 4. Thewobble press of claim 3 wherein said material is one of lead andtungsten carbide.
 5. The wobble press of claim 1 wherein a centeringdisk is arranged axially below and operatively interconnected with saidfirst wobbling die half, said centering disk couplingly centering saidfirst wobbling die half relative to said second die half.
 6. The wobblepress of claim 5, wherein said counterweight (G) is arranged axiallybelow said centering plate and is connected with said first die halfthrough openings in said centering plate.
 7. The wobble press of claim6, wherein said counterweight (G) annularly surrounds said second diehalf.
 8. The wobble press of claim 1, wherein said wobble drive of thefirst die half has at least three pump-working piston-systemssurrounding the wobble axis, and a multiple pump for supplying saidpump-working piston-system with cyclically varying amounts of oil. 9.The wobble press of claim 8, wherein said multiple pump has twooppositely acting axial piston pumps at equal axial location.
 10. Thewobble press of claim 8, wherein both of said axial piston pumps eachhave a wobble plate of fixed angulation, as well as each having a numberof pump pistons corresponding to the number of said working pistons,whose hydraulic conduits are connected in pairs with each other and witha pressure conduit of each assigned working piston.
 11. The wobble pressof claim 10, including means for the variation of the wobble stroke ofthe first die half, said means being provided via displacement of thephase location of both of said synchronously rotating pumps.
 12. Thewobble press of claim 10, including means for the variation of one ofthe number of revolutions and the direction of rotation of both pumpsfor attaining differing forms of wobble movement of said first die half.